Nitride semiconductor light-emitting device

ABSTRACT

A semiconductor light emitting device is provided. The semiconductor light emitting device includes a first nitride layer, an active layer, and a second nitride layer. The first nitride layer includes an irregular, uneven surface, and the active layer is formed on the irregular, uneven surface. The second nitride layer is formed on the active layer. A plurality of quantum dots are formed at the active layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/657,606 filed on Jan. 25, 2007 now U.S. Pat No. 8,253,151 claimingthe benefit of Korean Patent Application No. 10-2006-0008784 filed Jan.27, 2007, both of which are hereby incorporated by reference for allpurpose as if fully set forth herein.

BACKGROUND

1. Field of the Invention

The present invention relates to a nitride semiconductor light-emittingdevice, and a method for manufacturing the same.

2. Description of the Related Art

An example of a related art nitride semiconductor may include aGaN-based nitride semiconductor. The GaN-based nitride semiconductor isbeing applied to a variety of application fields such as an opticaldevice including blue/green light emitting diodes (LEDs), and afast-switching high-output device including a metal-semiconductor fieldeffect transistor (MESFET) and a high electron mobility transistor(HEMT). Particularly, the blue/green LEDs have already beenmass-processed, and the worldwide sales thereof are exponentiallyincreasing.

Particularly, in the field of light emitting devices such as LEDs andsemiconductor laser diodes among the application fields of the GaN-basednitride semiconductor, a semiconductor light emitting device thatincludes a crystal layer made by doping a Ga location of a GaN-basednitride semiconductor with the group 2 element such as magnesium andzinc is receiving much attention as a blue light emitting device.

As illustrated in FIG. 1, an example of the GaN-based nitridesemiconductor may include a light-emitting device having a multiplequantum well structure. The light-emitting device is grown on asubstrate 1 formed mainly of sapphire or SiC. For example, apolycrystalline thin film of Al_(y)Ga_(1-y)N is grown as a buffer layer2 on the substrate 1 of sapphire or SiC at a low growth temperature.Then, a GaN underlayer 3 is sequentially stacked on the buffer layer 2at a high temperature. An active layer 4 for light emission is placed onthe GaN underlayer 3. A magnesium (Mg)-doped AlGaN electron barrierlayer 5, a Mg-doped InGaN layer 6, and a Mg-doped GaN layer 7 that areconverted into a p-type by a thermal annealing process are sequentiallystacked on the active layer 4.

An insulating layer is formed on the Mg-doped GaN layer 7 and the GaNunderlayer 3, and a p-type electrode 9 and an n-type electrode 10 areformed corresponding to the Mg-doped GaN layer 7 and the GaN layer 3,respectively, thereby forming a light emitting device.

Such a related art light emitting device has the following problems.First, in the nitride semiconductor light-emitting device, latticemismatch exists between the substrate and the GaN, and thus many crystaldefects (surface defects, point defects, line defects) occur in ann-type nitride layer or a p-type nitride layer which has undergonecrystal growth. Hence, it becomes difficult to achieve good quality of acrystal layer.

Also, at the time of Mg doping for forming a p-type contact layer, Mg iscombined with H of an ammonia gas, thereby forming a Mg—H combinationhaving an electrical insulating property. Thus, even if a large amountof Mg is doped, it is difficult to achieve high hole-concentration in ap-type GaN.

In general, it has been known that quantum dots formed in InGaN and GaNepilayers used as an active layer take prominent part in increasingattention on the nitride semiconductor material as a high-output opticaldevice despite its disadvantages of dislocations, defects and anelectromagnetic field in a crystal. Such quantum dots perform stronglateral confinement or localization on carriers (electrons and holes) toremarkably reduce an influence of the dislocation or the electromagneticfield.

Specifically, electrons of a conduction band and holes of a valence bandin an active layer having a quantum well structure are trapped in thequantum dots, increasing the density states of the electrons and theholes in the quantum dots. Thus, light-emission recombination efficiencyof the electrons and the holes effectively increases. Also, a refractiveindex of the quantum dot is greater than a refractive index of asemiconductor material surrounding the quantum dot. For this reason,photons generated at the quantum dots are spatially trapped near to thequantum dots. Such an active layer structure of the light emittingdevice simultaneously confines both carriers and photons in the centerof an optical waveguide, so that a threshold current of the lightemitting device can be reduced approximately tens of times, andtemperature stability can be improved to an extent that allowsconsecutive operation of the light emitting device at a roomtemperature.

Accordingly, in order to improve light emission efficiency of thenitride semiconductor light-emitting device, it is most important todevelop a technology for controlling quantum dots of the active layer.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a nitridesemiconductor light emitting device and a method for manufacturing thesame that substantially obviate one or more problems due to limitationsand disadvantages of the related art.

The embodiment of the invention provides a nitride semiconductor lightemitting device capable of improving light emission efficiency bycontrolling the size and density of quantum dots and using a diffusedreflection effect of a surface of an n-type nitride layer, and a methodfor manufacturing the same.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

The embodiment of the invention provides a nitride semiconductor lightemitting device including: a first nitride layer including an irregular,uneven surface; an active layer on the irregular, uneven surface; and asecond nitride layer on the active layer, wherein the active layerincludes a plurality of quantum dots.

The another embodiment of the invention provides a method formanufacturing a nitride semiconductor light emitting device, including:forming a first nitride layer on a substrate, the first nitride layerincluding an irregular, uneven surface; forming an active layer alongthe irregular, uneven surface; and forming a second nitride layer on theactive layer.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a related art nitride semiconductorlight-emitting device;

FIG. 2 is a cross-sectional view of a nitride semiconductorlight-emitting device according to an embodiment of the presentinvention;

FIG. 3 is an enlarged view for describing a quantum dot area formed in anitride semiconductor light-emitting device according to an embodimentof the present invention; and

FIGS. 4 through 7 are cross-sectional views for describing a method formanufacturing a nitride semiconductor light-emitting device according toan embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a nitride semiconductor light emitting device and a methodfor manufacturing the same according to embodiments of the presentinvention will now be described with reference to accompanying drawings.

It will be understood that when a layer is referred to as being ‘on’another layer or substrate, it can be directly on the other layer orsubstrate, or intervening layers may also be present.

Although a nitride semiconductor light emitting device according to anembodiment of the present invention is applied to, for example, a lightemitting device having a quantum well structure (QW), the presentinvention may, however, be embodied in different forms and should not beconstructed as limited to the embodiment.

FIG. 2 is a cross-sectional view of a nitride semiconductorlight-emitting device according to an embodiment of the presentinvention.

Also, FIG. 3 is an enlarged view for describing a quantum dot area (A)formed in an active layer of a nitride semiconductor light-emittingdevice according to an embodiment of the present invention.

Referring to FIG. 2, the nitride semiconductor light emitting deviceaccording to an embodiment of the present invention includes a substrate11 of any one of sapphire, SiC or Si, a GaN buffer layer 12 of GaN onthe substrate 11, an un-doped GaN layer 13 on the GaN buffer layer 12, afirst n-type GaN layer 14 on the undoped GaN layer 13, the first n-typeGaN layer 14 having a rough (i.e., uneven) interface 15, an active layer16 on the interface 15, the active layer 16 including a plurality ofquantum dots 16-1, and a p-type GaN layer 17 on the active layer. Also,a thin second n-type GaN layer 18 may be further provided on the p-typeGaN layer 17. Thereafter, a p-type electrode 19 and an n-type electrode20 are provided for electrical connection, thereby completing a lightemitting device according to an embodiment of the present invention.

Here, although the active layer 16 is illustrated as just a layer inFIG. 2, the active layer 16 may include one or more wells 16-2 and abarrier 16-3 as illustrated in FIG. 3.

The semiconductor light-emitting device according to the presentinvention includes the first n-type GaN layer 14 including n-typedopants, and the active layer 16 formed of, for example, InGaN or thelike. A plurality of quantum dots 16-1 are distributed in the activelayer 16 formed along the interface 15. Here, in comparison with therelated art, those quantum dots 16-1 may be distributed at a higherdensity since more quantum dots are formed at an inclined area thanthose at a plane area by nature.

According to the present invention, the quantum dots 16-1 formed in theactive layer 16 with high density prevent defects, which are caused bylattice mismatch of nitride layers such as the substrate 11 and the GaNbuffer layer 12, from being transmitted to the active layer 16 and thep-type GaN layer 17. Thus, the formation of a faulty semiconductor layerhaving disadvantageous of, for example, defects or dislocation can beprevented.

Also, the quantum dots 16-1 laterally confine or localize carriers suchas electrons or holes, so that an influence of dislocation or anelectromagnetic field can be considerably reduced.

Accordingly, the characteristic of the active layer 16 is improved bythe plurality of quantum dots 16-1 formed at the active layer 16, sothat the light emission efficiency can be desirably improved.

Hereinafter, a process of manufacturing a nitride semiconductorlight-emitting device according to an embodiment of the presentinvention will now be described.

FIGS. 4 through 7 are cross-sectional views for describing a process ofmanufacturing a nitride semiconductor light emitting device according toan embodiment of the present invention.

Referring to FIG. 4, a GaN buffer layer 12 and an un-doped GaN layer 13are formed on a substrate 11. For example, the GaN buffer layer isformed at a temperature ranging from about 500° C. to 600° C. in a statewhere the substrate is mounted to a metalorganic chemical vapordeposition (MOCVD) reactor (not shown).

Ammonia (NH₃) and trimethyl gallium (TMG) are supplied on the GaN bufferlayer 12 at a growth temperature of about 1000° C. or higher. In thismanner, the un-doped GaN layer 13 including no dopants is formed on theGaN buffer layer 12 to a predetermined thickness.

Referring to FIG. 5, in order to form a first n-type GaN layer 14including n-type dopants on the un-doped GaN layer 13, a silane gasincluding n-type dopants such as NH₃, TMG and SI is supplied at a growthtemperature of, for example, about 1000° C. or higher.

After the first n-type GaN layer 14 is formed to a predeterminedthickness, the first n-type GaN layer is irregularly grown to form aninterface 15 having a predetermined irregular, uneven structure. A roughsurface of the first n-type GaN layer 14, that is, the interface 15 isformed such that the first n-type GaN layer 14 is irregularly grown bycontrolling the flow amount of NH₃ and the amount of n-type dopants atan atmosphere temperature ranging from about 500° C. to 800° C.

Here, in order to form the rough surface, that is, the interface 15, NH₃and n-type dopants are implanted in quantities of half the flow amountof NH₃ and double the amount of n-type as compared to quantities of NH₃and n-type dopants that form a flat n-GaN layer with the same thickness.In such a manner, the first n-type GaN layer 14 has the rough interface15.

The rough interface 15 of the first n-type GaN layer 14 causes aplurality of quantum dots 16-1 to occur at an active layer 16 to beformed later.

After the first n-type GaN layer 14 having the rough interface 15 isformed, as illustrated in FIG. 6, an active layer 16 is formed on thefirst n-type GaN layer 14.

The active layer 16 is formed by growing a layer to a predeterminedthickness at a growth temperature of about 780° C., using nitrogen as acarrier gas, for example, by supplying NH₃, TMG and TMIn. Here, thepredetermined thickness of the active layer 16 may be about 120 Å˜150 Åper one growth cycle.

Also, the active layer 16 may have a stacked structure including aplurality of layers through five to nine growth cycles if necessary.Here, as for the composition of the active layer having the stackedstructure, the layer may be grown with the molar fraction of eachelement, such as InGaN, varied.

During the active layer forming process, much more quantum dots 16-1 areformed by the rough surface, that is, the interface 15 of the firstn-type GaN layer 14. This is because more quantum dots 16-1 are formedby In on an inclined side than those on a plane side.

After the active layer 16 is formed, as illustrated in FIG. 6, a p-typeGaN layer 17 is successively formed on the active layer 16. Here, inorder to form the p-type GaN layer 17, for example, a Mg-based group 2element may be used for doping.

Thereafter, as illustrated in FIG. 2, a p-type electrode 20 may beformed on the p-type GaN layer 17. Portions of the p-type GaN layer 17,the active layer 16 and the first n-type GaN layer 14 are etched toexpose the first n-type GaN layer 14. Thus, an n-type electrode 20 formsan electric contact on the first n-type GaN layer 14.

In another embodiment of the present invention, as illustrated in FIG.7, a thin second n-type GaN layer 18 may be further grown on the p-typeGaN layer 17.

As described so far, in the nitride semiconductor light-emitting device,and the method for manufacturing the same according to an embodiment ofthe present invention, the rough interface 15 having an irregular,uneven structure is formed between the active layer 16 and the firstn-type GaN layer 14. The rough interface 15 serves to increase thedensity of quantum dots 16-1 formed at the active layer 16, therebyimproving light emission efficiency.

Also, according to the present invention, the quantum dots 16-1 obviatelattice mismatch, thereby achieving good quality of an active layer 16.Also, a diffused reflection effect of light generated from the activelayer 16 can occur by the interface 15 with the rough surface, so thatthe light emission efficiency can be further improved.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A semiconductor light emitting device,comprising: a first gallium nitride based semiconductor layer; an activelayer on the first gallium nitride based semiconductor layer, the activelayer including at least one uneven structure, the at least one unevenstructure having first inclined surfaces; and a second gallium nitridebased semiconductor layer on the active layer, wherein the active layercomprises: a plurality of vertical distances of different thicknesses; awell layer; a barrier layer; and a first In-rich region at the firstinclined surfaces of the uneven structure, wherein the well layercomprises the first In-rich region at the first inclined surfaces of theat least one uneven structure, wherein the well layer comprises a firstwell region where the first In-rich region is not formed, and wherein anIn density of the first In-rich region at the first inclined surfaces ishigher than an In density of the first well region.
 2. The deviceaccording to claim 1, wherein the first gallium nitride basedsemiconductor layer comprises a second inclined surface.
 3. The deviceaccording to claim 2, wherein at least one of the first inclinedsurfaces of the uneven structure and the second inclined surface of thefirst gallium nitride based semiconductor layer has vertices ofdifferent heights.
 4. The device according to claim 2, wherein adistance between an uppermost portion of the second inclined surface anda lowermost portion of the second inclined surface in a verticaldirection is greater than a thickness of the one period of the activelayer.
 5. The device according to claim 1, wherein the first galliumnitride based semiconductor layer comprises second inclined surfaceswith the active layer, the second inclined surfaces formed byprotrusions.
 6. The device according to claim 5, wherein at least one ofthe first inclined surfaces of the uneven structure and the secondinclined surfaces of the first gallium nitride based semiconductor layercomprise at least one substantially V shape in a sectional view.
 7. Thedevice according to claim 6, wherein a side opposite a vertex of the atleast one substantially V shape contacts the second gallium nitridebased semiconductor layer.
 8. The device according to claim 5, whereinthe second inclined surface of the first gallium nitride basedsemiconductor layer contacts the first uneven structure of the activelayer.
 9. The device according to claim 5, wherein the first inclinedsurfaces have the at least one substantially V shape in a sectionalview, the at least one substantially V shape has a vertex, and thevertex of the first inclined surfaces is positioned towards the firstgallium nitride based semiconductor layer or contacts the first galliumnitride based semiconductor layer.
 10. The device according to claim 1,wherein the second gallium nitride based semiconductor layer comprises athird inclined surface.
 11. The device according to claim 10, whereinthe third inclined surface of the second gallium nitride basedsemiconductor layer contacts the first uneven structure of the activelayer.
 12. The device according to claim 1, wherein the at least oneuneven structure is formed irregularly.
 13. The device according toclaim 1, further comprising a substrate under the first gallium nitridebased semiconductor layer, the first gallium nitride based semiconductorlayer having protrusions, wherein the first gallium nitride basedsemiconductor layer extends from the substrate to the protrusionswithout an intervening interface.
 14. The device according to claim 1,wherein the at least one uneven structure comprises a rough surface. 15.The device according to claim 1, further comprising: a substrate; abuffer layer on the substrate; and an un-doped gallium nitride basedsemiconductor layer on the buffer layer, wherein the first galliumnitride based semiconductor layer is on the un-doped gallium nitridebased semiconductor layer.
 16. The device according to claim 1, furthercomprising a third gallium nitride based semiconductor layer on thesecond gallium nitride based semiconductor layer.
 17. The deviceaccording to claim 1, wherein the active layer comprises a secondIn-rich region therein, wherein the second In-rich is not formed in thefirst well region, and wherein an In density of the second In-richregion is higher than the In density of the first well region.
 18. Thedevice according to claim 1, wherein at least one of the first inclinedsurfaces of the at least one uneven structure comprises at least one Vshape having a sharp edge in a cross-sectional view, and wherein thefirst In-rich region is disposed on the sharp edge.
 19. The deviceaccording to claim 1, wherein the first gallium nitride basedsemiconductor layer comprises a plurality of protrusions, and whereintop surfaces of the plurality of protrusions contact with a bottomsurface of the at least one uneven structure of the active layer. 20.The device according to claim 1, further comprising a third galliumnitride based semiconductor layer on the second gallium nitride basedsemiconductor layer, wherein the third gallium nitride basedsemiconductor layer is thinner than the second gallium nitride basedsemiconductor layer.
 21. The device according to claim 20, wherein thefirst gallium nitride based semiconductor layer comprises a first n-typeGaN layer, wherein the second gallium nitride based semiconductor layercomprises a p-type GaN layer, and wherein the third gallium nitridebased semiconductor layer comprises a second n-type GaN layer.